1. Field of the Invention
This invention relates to a process for the oxidation of an aromatic compound selected from benzene and biphenyl compounds containing at least one isopropyl group, in which the aromatic compound is oxidized with molecular oxygen to convert at least one of said at least one isopropyl group into a 2-hydroxy-2-propyl group.
The benzene or biphenyl compound, which is prepared in accordance with the process of this invention and contains at least one 2-hydroxy-2-propyl group, can be converted into a benzene or biphenyl compound containing at least one hydroxyl group bonded directly to the aromatic ring by a process similar to that disclosed in the specification of Japanese Patent Application No. 123819/1985 on naphthalene derivatives. It is therefore possible to prepare, for example, hydroquinone from p-diisopropylbenzene or resorcine from m-diisopropylbenzene by practising successively the process of this invention and a process similar to that disclosed in the specification of Japanese Patent Application No. 123819/1985 on naphthalene derivatives.
2. Related Art
A variety of processes, including those to be described below by way of example, has heretofore been known to oxidize one or more side-chain isopropyl groups of a benzene ring with molecular oxygen in the presence of an aqueous alkali solution so as to convert said one or more side-chain isopropyl groups into the corresponding number of 2-hydroxy-2-propyl groups.
(1) Cumene or diisopropylbenzene is oxidized in the presence of an aqueous sodium carbonate solution and cobalt naphthenate to obtain a 2-hydroxy-2-propyl derivative [JOURNAL OF THE FUEL SOCIETY OF JAPAN, 35, 518-525 (1956)].
(2) An aryldialkylmethane is oxidized in the presence of an aqueous caustic alkali solution and a manganese salt to obtain an .alpha.-aryl tertiary alcohol (Japanese Patent Publication No. 19355/1964).
(3) A tertiary hydrogen is oxidized in the presence of an aqueous caustic alkali solution to obtain an aralkyl carbinol (Japanese Patent Publication No. 21242/1964).
(4) Diisopropylbenzene is oxidized in the presence of an aqueous caustic alkali solution to obtain a 2-hydroxy-2-propyl derivative (Japanese Patent Laid-Open No. 59827/1976).
(5) An aryldialkylmethane is oxidized in the presence of an aqueous alkali solution, and the feeding of oxygen is stopped and the reaction mixture is heated, thereby decomposing a hydroperoxide byproduct and obtaining an .alpha.,.alpha.-dialkylbenzylalcohol (Japanese Patent Laid-Open No. 162539/1983).
(6) An aryldialkylmethane is oxidized in the presence of an aqueous alkali solution and a transition metal compound to obtain an .alpha.-aryl tertiary alcohol (Japanese Patent Laid-Open No. 162540/1983).
(7) Diisopropylbenzene is oxidized in the presence of an aqueous alkali solution to obtain a mixture composed principally of a dihydroperoxide, followed by reduction of the mixture to obtain di(2- hydroxy-2-propyl)benzene (Japanese Patent Laid-Open Nos. 149538/1985, 152431/1985 and 85340/1986). By these processes, the conversion of one or more side-chain isopropyl groups of a benzene ring into the corresponding number of 2-hydroxy-2-propyl groups has been effected.
However, each of the above processes (1), (2) and (6) results in considerable coloration of its reaction product due to the use of the transition metal compound, thereby making it difficult to purify the intended compound. The above process (3) uses the aqueous caustic alkali solution of a high concentration in order to suppress the byproduction of hydroperoxides. The process (3) is however not considered to be able to inhibit the byproduction of such hydroperoxides completely. The above process (4) is not considered to be an effective process for general purposes, because the composition of its raw materials is limited. The above process (5) is disadvantageous from the viewpoint of production cost, since heating is effected after completion of the oxidative reaction in order to suppress the byproduction of hydroperoxides like the process (3). The above process (7) is disadvantageous economically, because it requires accumulation of the instable hydroperoxide at a high concentration, the byproduction of ketone compounds due through decomposition of the hydroperoxide is not ignorable, and the two-step reaction is carried out.